In a virtualized machine environment, one or more virtual machines may operate on a server simultaneously. Memory associated with one or more of the virtual machines may need to be mirrored. For example, a mirrored virtual machine may be useful for fail-over redundancy from one virtual machine to another virtual machine, or may be useful to recreate one or more virtual machines at a particular state or a particular point in time. Mirroring virtual machines may also be useful for debugging purposes.
A checkpointed mirroring process may create a snapshot of memory accessed by a virtual machine during multiple points in time, also known as epochs. An epoch may include a time for processing and a time for creating a checkpoint of the memory at a conclusion of the processing time. Checkpointing memory of a target virtual machine may also be useful for debugging or to create redundancy. It may be inefficient, both in terms of memory used and also in terms of time used, to create a complete copy of each memory page available to a virtual machine during every epoch. A more efficient use of time and memory may be to implement dirty page logging (“DPL”).
A DPL system for checkpointing virtual machine memory may check each memory page to see if a page has been modified since a prior epoch. If the page has not been modified, then the DPL system may not mirror the page. If the page has been modified since the last epoch, then the DPL system may create a copy of the memory page for mirroring. In this manner, only pages changed from a prior epoch may be mirrored, so DPL implementation may save memory, while maintaining a complete checkpoint of the state of virtual machine memory at each epoch.
A problem associated with the above-described memory logging technology is that all of the memory may be placed in a read-only state at the beginning of each epoch, and attempts to write to a memory page may create a memory management unit (“MMU”) fault. This fault may be generated for the first memory page write attempt to a new memory page in an epoch. At the beginning of a new epoch, all memory pages are again made read-only, and the process may begin again. MMU faults may have an adverse impact on the overall performance of the virtual machine, and on hypervisors and physical servers as well.
In view of the foregoing, it may be understood that there are significant problems and shortcomings associated with current memory logging technologies.